Improper use of flaps by 172 pilot

What reportedly happened: The airplane, which took off from a 2,350-foot runway with tall trees located off the departure end, was loaded with full fuel, the pilot and three passengers. It was about 117 pounds below its maximum gross operating weight at takeoff.

The pilot selected 10° of flaps for takeoff,however, the owner’s manual stated that normal and obstacle clearance takeoffs in that model were to be performed with wing flaps retracted and specified the use of takeoff flaps only for soft or rough fields.

Just after liftoffat an altitude of about 40 feet AGL, the airspeed began to deteriorate and the stall warning sounded. The pilot turned to the left in an attempt to avoid the trees at the end of the runway, but it was not enough to keep the airplane’s right tire from hitting a tree. The pilot was able to land on a nearby road.

During the landing roll, the left wing hit a tree, causing the airplane to swerve to the left, and the nose landing gear to shear off before the airplane slid to a stop.

Investigators determined the pilot’s improper use of flaps during takeoff while operating near the airplane’s maximum gross weight reduced the airplane’s climb capability and it was unable to clear the trees off the end of the departure runway.

Probable cause: The pilot’s improper use of flaps for takeoff, which resulted in the airplane’s failure to attain adequate climb airspeed and subsequent collision will trees during takeoff.

Comments

I had a 1973 Cessna 172, I think it was a “M” model. Irregardless. I would like to know the weights of the pilot, and the three passengers. I just don’t see how they could have full fuel, all those people and still be 117 or so pounds under gross weight. I hope they were. My gut feeling says that seems like a lot of weight.

Might have asked too much of the 172. With all of those bodies it might have been prudent to depart with a reasonable fuel load. Temp & elevation likely had something to do with it. Better to err on the conservative side.

What was not stated in this scenario was what type of surface the aircraft departed on. Chances are it was grass. And were the “tall trees” located just off the runway end, or was the 2350 ft. runway provided a 20:1 approach to the runway end (which is an FAA Standard to negate the normal placement of a displaced threshold which would effectively reduce the runway length). A detailed analysis of these physical conditions/layout is reported by the Designated Airport Inspector for the purposes of AF/D reporting, assuming this was a public-use airport. If “private-use”, anything goes, which means, who knows how many feet (distance) existed between advancing the throttle and the tree top. Of course, the abbreviated AF/D doesn’t report everything the Inspector reports either. If you want the true (complete) version (and pertinent information), get on the internet and go to AirNav.com and you will then learn just how far the obstruction height is from the runway end and how far off runway centerline.

The previous was a bit of info most pilots don’t know and don’t care. They should. But addressing the use of flap situation, I’ve always told my students that ANY amount of flap extension will reduce the rate of climb, i.e., the drag from flap extension will reduce the climb gradient. Of course, if the runway was grass … (height?), one might consider the use of some flap just to ‘break’ ground. A matter of judgement and perhaps the aircraft involved. The PTS, with all it’s verbal garbage, I don’t think addresses all of the takeoff scenarios. From a former airport inspector and a CFII for 54 years.

Dale – thanks for commenting. I am a relatively new pilot and I learned on a runway that is just under 2500ft. That was always called a short field takeoff and in the checklists it ALWAYS calls for 10 deg. Flaps for short field. I am confused by this report.

Who wrote the check list? What is the rate of climb at best angle with and without flaps? My experience indicates that people misuse flaps on takeoff because they do not understand or practice what the POH states. Many times they got their information from an instructor that teaches in many types of airplanes and is not an expert in any model. I have a friend that always uses 10 degrees of flaps for takeoff in his Bonanza. He believes it’s safer. There is too much mis information out there. If the lawyers put it in the POH, it has to be true..

The Cessna POH says use 10 degrees flaps. It also says “using 10 degrees flaps reduces ground roll and distance over an obstacle by approximately 20 percent” I don’t understand the determination of improper use of flaps unless it was a different model year though I am fairly certain that all 172s have a 10 degree flap setting for short field take off

The newer 172’s use 10 degrees for short-field takeoffs – older ones like a C172N use 0 (zero) degrees. A Piper Warrior uses 25 degrees. It’s important to check the manual and know what is correct.
The report indicates the stall warning sounded. That would be caused by one thing – the pilot did not maintain the proper pitch and airspeed with the elevator, no matter what the configuration was. On departure if the pilot sees an obstacle ahead, it is easy to understand that he may pitch the airplane a little too high in an effort to climb at a steeper angle. If this happens, the speed will fall below Vx and will cause the climb performance to deteriorate because the induced drag is higher than it would be at Vx. It is critical that this is corrected immediately. For example, maybe the nose is raised to a 13 degree pitch but what is needed to maintain Vx is 8 degrees of pitch under all of the conditions (weight/density altitude) at that moment. At the 13 degrees of pitch, the pilot may notice from outside references that the climb angle will not clear the obstacle, and pitch up more. This will result in lower airspeed even further from Vx, and even higher induced drag and worse climb performance. You can see now this process will result in yet worse and worse climb performance and eventually a stall.

Whereas, if the pitch had been smoothly corrected to 8 degrees originally, then the airplane would establish and maintain Vx. It is a little counter-intuitive to improve climb performance by reducing the pitch, but that may be what you have to do to realize the best angle of climb. The recommended technique when changing the pitch is to look at a pitch reference such as the horizon or the attitude indicator, make the pitch change, and then give the airspeed a few seconds to react. If you change the pitch while fixating on the airspeed indicator, it is easy to over-correct.

Since this report indicates the stall warning sounded, it appears the problem was more likely the pitch control and not the flaps extended to 10 degrees.

Why does Cessna in the poh for C172 from 1981 to 2001 state on the short field takeoff checklist 10 degrees of flaps and climb at 56 kias “UNTIL ALL OBSTACLES ARE CLEARED”. Best angle of climb is 60 ktas the 56 is kias. Of course the specific year of the aircraft was not mentioned, but full fuel and three passengers suggests an older 172, the R model on up have only 830 lbs useful load

Christopher – you may see three specific speeds in some POH’s for the short-field takeoff where the most precision is the objective. First the lift-off speed may be specified – that is basically the same as the rotation speed although some pilots may rotate a knot or two earlier to literally ‘lift-off’ from the surface at the published airspeed. The second speed is what should be indicated a 50 ft. and will not necessarily be Vx. I believe the purpose of that number is to help manage the pitch of the airplane from the ground to 50 ft. In other words, you wouldn’t want to break ground and then accelerate to Vx in near level flight. You will get the maximum separation from the obstacle by managing the airspeed from the first number to the second number in the first 50 ft. This is the result that factory flight testing would have found. The third number will be basic Vx, which the airplane’s performance may not even be able to reach until after flying through 50 ft if the proper procedure is followed from the first to the second number. Remember to adjust the Vx higher for higher pressure altitude per the POH, and add a gust factor if appropriate. I’ve always seen these speeds as indicated (KIAS), not true (KTAS).

Dale – I agree that any amount of flap extension will increase drag and reduce the rate of climb. However the short field takeoff POH procedure ties several techniques together – configuration, pitch attitude on the takeoff roll (slightly tail low), and a specific lift off speed. All together, this will normally mean a liftoff much sooner, or said another way, much further away from the obstacle. Even though the rate of climb may suffer a very small amount from the 10 degrees of flaps, the overall distance from the obstacle passing through 50 ft will be greater.